1. Field of the Invention
The present invention relates to a photometering lens of a single lens reflex (SLR) camera, and in particular, it relates to a structure of a photometering lens incorporated in a photometering device in an SLR camera and an adjusting method of the photometering device.
2. Description of the Related Art
In a known type of photometering device for an SLR camera, light transmitted through a finder screen (focusing screen) is received by a light receiving element to measure the brightness of an object.
The basic structure of a conventional SLR camera and photometering lens is shown in FIGS. 10 and 11. A camera body 101 is provided with a photographing lens 103 which is detachably attached thereto. Light carrying an object image incident upon the photographing lens 103 is partly transmitted through a main mirror 105 and is reflected by a sub-mirror 107 toward an AF sensor unit 109. The object light incident upon the photographing lens 103 is partly reflected by the main mirror 105, is converged onto a finder screen (focusing screen) 31 to form (or project) an object image thereon, and passes through the finder screen 31. The finder screen 31 is located at a position which is optically equivalent to a film surface 111. The object light passing through the finder screen 31 is reflected by a hollow pentagonal mirror (a reflecting optical member) 21. The light reflected by the hollow pentagonal mirror 21 partly passes through an eyepiece 41 and is partly transmitted through a photometering lens 11' and is received by a light measuring receiver (a light receiving element) 13. The hollow pentagonal mirror 21 can be replaced by a pentagonal prism per se known.
In the SLR camera mentioned above, position of the light measuring receiver 13 is adjusted to coincide with the image of the finder screen 31. In particular, in case that the light measuring receiver 13 is a center-weighted measuring type or a divided brightness measuring type, it is necessary to precisely make the image of the finder screen 31 coincidental with the light receiving area (measuring area) of the light measuring receiver 13. Namely, the centering operation to register the center of the object image on the finder screen 31 with the center of the central light receiving element of the light measuring receiver 13 must be precisely carried out.
To this end, in the prior art, the relationship between the light measuring receiver 13 and the measuring area is adjusted in such a way that a reference chart is placed in a predetermined position on the optical axis and the position of the photographing lens is adjusted with respect to the reference chart. The output of the central light receiving element of the light measuring receiver 13 is measured while moving the light measuring receiver 13. The position in which the output of the central light receiving element of the light measuring receiver 13 becomes maximum corresponds to the center position.
However, in this adjustment, since the output of the light measuring receiver is measured while moving the light measuring receiver 13, it takes a long time to detect the peak value of the output.